1. Technical Field
The present invention relates generally to head suspensions for supporting read/write heads over recording media. In particular, the present invention is directed to head suspensions having vibration absorption structures particularly effective at resonance frequencies.
2. Background of the Invention
Head suspensions are well known and commonly used within dynamic magnetic or optical information storage devices or drives with rigid disks. The head suspension is a component within the disk drive which positions a magnetic or optical read/write head over a desired position on the storage media where information is to be retrieved or transferred. Head suspensions for use in rigid disk drives typically include a load beam that generates a spring force and supports a flexure to which a head slider supporting a read/write head is to be mounted. The load beam typically includes a base at a proximal end, a rigid region at a distal end, and a spring region between the rigid region and the base for providing the spring force. The head slider is aerodynamically designed so as to allow the read/write head to "fly" on an air bearing generated by the spinning magnetic or optical storage disk against the opposing spring force. The flexure permits pitch and roll motion of the head slider and read/write head as they move over the data tracks of the disk. Head suspensions are normally combined with an actuator arm to which the base of the load beam is mounted so as to position (by linear or rotary movement) the head suspension, and thus the head slider and read/write head, with respect to data tracks of the rigid disk.
With the advent of more powerful computers and the rapid growth in the personal computer market, it has become increasingly more important to enable the user to store and access data to and from storage devices with increased speed and accuracy. Because of this need to reduce access times to enable rapid storage retrieval of data it has become increasingly more important to reduce undesirable levels of vibration of components within the rigid disk drive.
In relation to this, an important consideration in the design of head suspensions is resonance characteristics; that is, the head suspension's performance at its resonance frequencies. Resonance characteristics of a head suspension are particularly important because a head suspension is more sensitive to vibrations at a resonance frequency thereof than to vibrations at non-resonance frequencies. That is, if the servo system, or other portion of the ambient environment external to the head suspension and coupled to the head suspension via the actuator arm, is vibrating or causes vibration of the head suspension at a frequency at or near a resonance frequency of the head suspension, the resulting vibration of the head suspension will be at its resonance frequency. The amplitude of the movement of this vibration at the head slider will be greater than if the servo system, and therefore head suspension, were vibrating at a non-resonance frequency. That is, the gain (the ratio of the amplitude of the motion of a head suspension at the head slider to the amplitude of the motion input into a head suspension at its base) of a head suspension is significantly larger when the input motion is a vibration at a resonance mode frequency of the head suspension than when the input is a vibration at a non-resonance mode frequency thereof Further, if an impulse force is imparted to the head suspension, as opposed to an ambient vibration or electrically induced, vibration in the head suspension at resonance mode frequencies can naturally result. Such an impulse force could be caused by quickly stopping the head suspension over a data track to read or write information as well as by an externally applied force.
Because vibration of a head suspension at a resonance mode frequency can have large gain, such vibrations can cause delay in the read/write process. Specifically, vibrations of the head suspension at a resonance mode frequency may delay the transfer of data because the data cannot be confidently transferred until the amplitude of the movement of the head slider has substantially decayed.
Of particular importance are the first and second torsion resonance modes and lateral bending (or sway) resonance mode of vibration. These resonance modes can result in lateral movement of the head slider at the end of the head suspensions and are dependent on cross-sectional properties along the length of the load beam. The torsion modes sometimes produce a mode shape in which the tip of the resonating head suspension moves in a circular fashion. However, since the head slider is maintained in a direction perpendicular to the plane of the disk surface by the spring force of the load beam acting against the air bearing, lateral motion of the rotation is seen at the head slider. The sway mode is primarily lateral motion. The first torsion resonance mode is of particular importance because it usually occurs at frequencies which are low enough to be commonly encountered in rigid disk drive head suspensions (typically below 5000 Hz).
Approaches to minimize the effect of resonance modes include designing the head suspension so that certain resonance modes are high enough so as not to be excited within a particular disk drive or to minimize the movement of the head slider or gain that results from one or more resonance modes(s). The latter can be accomplished by designing the head suspension so that gain is minimal or by damping the movement.
The use of dampers on head suspensions to decrease gain at resonance mode frequencies is generally known and described, for example, in U.S. Pat. Ser. No. 5,187,625 issued to Blaeser et al. on Feb. 16, 1993 ("Blaeser") and U.S. Pat. Ser. No. 5,299,081 issued to Hatch et al. on Mar. 29, 1994 ("Hatch").
Both Blaeser and Hatch disclose the use of elastic and visco-elastic damping materials located on a part of the head suspension to absorb vibrations. However, use of such materials often necessitates the addition of curing or out-gassing steps to the fabrication process. Further, the use of such materials requires care to prevent the attraction of contaminants both during the fabrication process and during in situ use. Also, such damping materials typically require the addition of a constraint layer of stainless steel or other rigid material over an exposed surface of the damper. As such, use of these types of dampers can add significant mass to the head suspension. Added mass (depending upon where it is localized) can increase the time required for vibrations of the head suspension to decay and, thus, increase information access times. Further, adding viscous material to a head suspension can add steps to the manufacturing process, slowing the process and increasing costs.